How Many Ways can a Substrate be Chemically Protected?

protective metal finishes series

When you put a piece of steel in an acid, it reacts by corroding and rusting because the iron ions in the steel are soluble in acidic solutions.

Similarly, when you put iron in an alkaline solution, it reacts by corroding because the iron ions are also soluble in alkaline solutions.

However, putting iron with a small amount of chromium in an acid won’t react much.

There are several reasons for this, which we’ll explore below.

What is Chromium?

Chromium is a transition metal belonging to the group 16 elements, with a shiny, silver-colored appearance, and is brittle and soft. It is an essential trace element for humans, but large amounts can be poisonous. Found in rocks, soil, and seawater and extracted commercially, chromium is the third-most-abundant element in the Earth’s crust, after iron and oxygen.

Many industries use chromium, such as cement, pigments, and dyes, but the most important use is stainless steel. Other alloys use chromium, such as nickel/chromium alloys and chromium-plated metals, chrome-plated plastics, and as a coating of iron and steel. Other industries, such as the chemical industry, use chromium to produce dyes, pigments, and other products and electroplate metals. It is also used to make car parts, brake pads, and other components.

How does Chrome Corrosion Protection work?

As we have discussed above, when placing a piece of steel with a small amount of chromium in acid, there isn’t much reaction for several reasons:
Chromium is less reactive than iron, meaning that it does not readily react with other elements; It forms a stable oxide on its surface called CrO, and oxygen stops the corrosion process of chromium.

When a thin layer of chromium forms on the surface of the steel, it protects it from corrosion by blocking oxygen, water, and other elements from the metal.
It is an electrochemical process that creates a passive barrier on the metal surface that shields it from the environment, which is how chrome corrosion protection works!

Chrome Electroplating

Chrome electroplating is electroplating chromium metal to the surface of a metal substrate, such as steel, stainless steel, and nickel, with an electrolyte and a current, applied to the metal object. Electromagnetic force attracts chromium ions and deposits them on the metal surface, resulting in a thin and dense layer of chromium. Electroplating protects metals against corrosion, improves their appearance, strengthens them, and makes them more durable, which is why it’s mostly applied to car parts, rims, bike parts, electrical components, and other metals.

North Star Plating shows the plating process:

Chrome Coating Slurry and Sludge Media-Coated Steel

When applying electroplating with a slurry or sludge media-coated steel, depositing a thin layer of chromium on the metal surface protects it from corrosion—depositing a plating layer on the metal surface when applying a current, resulting in a thin and dense layer of chromium.

The electroplating process uses cyanide, used to produce chromium. When mixing cyanide with water and applying it to the metal, it forms an electroplated chromium layer, resulting in a thin and dense layer of chromium.

How Does Chrome Electroplating Protect?

When that thin layer of chromium forms on the steel’s surface, it protects it from corrosion by blocking oxygen, water, and other elements from the metal, which is how chrome electroplating acts as a protective coating. Electroplating chromium to the steel’s surface creates a passive barrier on the metal surface that shields it from the environment.

This passive barrier is not a passive coating, but an electrochemical process. There are variations in the chromium’s thickness coating depending on the voltage and current used in the plating process. The thicker the coating, the more durable and longer-lasting it is. However, even with a thin coating, chromium protects the steel from corrosion for years, if not decades.

In Sum

Chromium is a transition metal that also belongs to the group 16 elements. It has a shiny, silver-colored appearance and is brittle and soft. When a thin layer of chromium forms on the surface of the steel, it protects it from corrosion by blocking oxygen, water, and other elements from the metal.

This is how chrome electroplating acts as a protective coating.

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